Noise
and Vibration Studies

The Technical Noise Supplement (TeNS) to the Traffic Noise Analysis Protocol has been updated. As of July 2011, 23CFR 771 requires TNM analysis for all Activity Category Land Uses. Much of the technical content remains unchanged, but all references to older noise models have been removed. Other changes include the renumbering of chapters, figures, equations, and tables.

This manual contains Caltrans noise analysis procedures, practices, and other useful technical background information related to the analysis and reporting of highway and construction noise impacts and abatement. It supplements and expands on concepts and procedures referred to in the Traffic Noise Analysis Protocol, which in turn is required by federal regulations in 23CFR772. The contents of this document are not official policy, standard, or regulation, and are for informational purposes—unless they are referenced in the Protocol. Except for some Caltrans-specific methods and procedures, most methods and procedures recommended in this document are in conformance with industry standards and practices. This document can be used as a stand-alone guide for highway noise training purposes or as a reference for technical concepts, methodology, and terminology needed to acquire a basic understanding of highway noise and construction noise-related issues.

The Transportation and Construction Vibration Guidance Manual has been updated and expanded. The new PDF version is indexed for easier searching. This manual provides practical guidance to engineers, planners, and consultants who must address vibration issues associated with the construction, operation, and maintenance of Caltrans projects.

The Caltrans Sound Wall Inventory

Is available for viewing at the Statewide Soundwall Inventory web page. This sound wall inventory is prepared for information collection purposes for the FHWA as required by federal code in 23 CFR 772.

FHWA approved the new California DOT noise policy (Protocol) (1.03MB) for new or reconstruction highway projects. This new Protocol becomes effective on July 13, 2011 for all Federal Aid projects. The change is required under the revised Title 23, Part 772 Federal Code which became effective July 13th, 2010. This Protocol contains many new provisions including the criteria for grandfathering existing projects currently under development. Following is a partial list of revised criteria:

Activity Categories - the categories have changed eliminating an interior requirement for residences. There is no longer a severe impact (75 dB) and so no longer "extraordinary abatement". There is an interior requirement for public buildings of 52 dB - we will look at outside noise and predict insertion loss of building facade. We will now be looking more consistently at sports facilities, campgrounds and other recreation areas.

New "Design Goal" of at least 7 dB reduction for one benefited receptor per wall.

Reasonableness - we now have a formalized approach to voting for renters and owner occupied residences. There is a much simpler reasonable allowance of $55,000 per benefited receptor - this includes non residential such as recreation areas, hospitals etc. where impacts are predicted.

Type II (Retrofit noise abatement) - Caltrans will work with COGS to develop a prioritization procedure for all federally reimbursed Type II projects. This is an FHWA requirement.

Recent Activities

Quieter Pavement Studies Updated

Quieter Pavement studies are on-going. These studies demonstrate that pavement acoustics vary with pavement parameters and these studies track how the acoustics change with time. Sometimes, acoustical differences between various types of pavements can be significant - age, environment, and traffic loads also factor into the acoustic behavior. Portions of this material have been presented in various forms at conferences such as TRB, INCE, InterNoise, and SAE during the last decade. Three different pavement acoustic measurement procedures have been developed from this work and are being drafted as AASHTO Standards:
1) Onboard Sound Intensity (OBSI) Measurement,
2) Continuous Time Integrated Measurement (CTIM), and
3) Stastical Isolated Pass-By (SIP) Measurement. Several long-term studies have recently been updated and are available for downloading :

The I-80 Davis OGAC Pavement Noise Study is the longest running quiet pavement study in the nation. This study definitively demonstrated that pavement selection can impact roadside noise levels and the acoustic benefits of quieter pavements lasts much longer than a couple of months or years. At this site an aged and worn flexible pavement was replaced with an OGAC and before and after wayside noise measurements were taken. OBSI measurements were added to the measurement series in September 2002, after the new technique was developed. The wayside measurement process would later be used as a reference to develop the AASHTO CTIM Measurement Standard. Seasonal and meteorological variations were also tracked in this lengthy, 12 Year study.

This long-term study focused on acoustic characteristics of several typical flexible pavements used by Caltrans. On a relatively quiet two-lane road in the high desert, 80 miles north of downtown Los Angeles, five different pavements were placed adjacent to each other and exposed to the same traffic loads in the same environment. The pavements included a Dense Graded Asphalt Concrete (DGAC 30mm thickness), an Open Graded Asphalt Concrete (OGAC 30mm thickness), a thicker OGAC (75mm), a Rubberized Asphalt Concrete - type Open-Graded (RAC-O 30 mm thickness),and a Bonded Wearing Coarse (BWC). Noise levels were measured at the tire/pavement interface, at the roadside, and in the vehicle interior. [Notes: Caltrans has renamed some of these pavements since this project started, but this report retains the original naming convention. It has been determined that the BWC OBSI noise level was atypically higher than other BWC sites in the state.]

This long-term study focused on acoustic characteristics of various rigid pavement surface textures. This test section is located on the four lane divided Mojave-58 Bypass which carries a growing amount of heavy truck traffic. This site is also in the high desert, about 40 miles from the LA-138 flexible pavement site. Several base textures were evaluated initially and then grinding and grooving variations were added and measured. Follow-up OBSI measurements were taken to monitor acoustic changes.

European research into quieter pavements preceded work in the USA by more than a decade and their measurement equipment requires a vehicle pulling a specialized trailer. The US measurement equipment bolts to the wheel lugs and requires only a standardized test tire -- making the USA AASHTO OBSI measurement approach much less expensive and very portable. The NITE, or Noise Intensity Testing in Europe, Study was the first definitive side-by-side comparison of European and American (CA and AZ) quiet pavements - all measured with the same equipment, by the same operator, under similar operating conditions. Even though the European community had spent more time experimenting with acoustically optimized pavements, standard off-the-shelf pavements in the USA compared very favorably to European low noise pavements.

The Volpe Center Acoustics Facility also measured the various flexible pavements at the LA-138 site. At the time of this study, Volpe conducted only Statistical Pass-By measurements (based on an ISO draft standard) and examined the effects of pavement noise relative to overall vehicle noise levels at the roadside. Volpe measured how the noise propagated from the vehicles on the road to distant receivers. The extensive data set from this study is referenced for on-going improvements to the FHWA Traffic Noise Model and used for developing the AASHTO SIP Measurement Standard.

Much of the knowledge from these noise studies was applied to constructing low noise pavement surfaces on the new San Francisco Oakland Bay Bridge. Both the Skyway and Oakland Touchdown portions of the bridge have used pavement textures designed to lower traffic noise levels. This is particularly beneficial for the pedestrians and cyclists using the impressive sidewalk to Yerba Buena Island. See project images below.

Images from the LA-138 test site below:

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Publications

Noise and Vibration Technical Advisories
have been posted at the publications web page.

The following publications pertaining to
acoustical and vibration issues are available for downloading:

Training Resources

The Division of Environmental Analysis
has several on-line noise
training modules for use by the public. These modules cover highway traffic noise fundamentals, noise measurements and instrumentation, noise analysis procedure, and design of noise barriers. This training was published in 2002 and some of the content may be superceded.